MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
Freescale Semiconductor
22-11
6
SOFTRST
Soft reset. When asserted, FlexCAN2 resets its internal state machines and some of the
memory-mapped registers. The following registers are affected by soft reset:
• CANx_MCR (except the MDIS bit),
• CANx_TIMER,
• CANx_ECR,
• CANx_ESR,
• CANx_IMRL,
• CANx_IMRH,
• CANx_IFRL,
• CANx_IFRH.
Configuration registers that control the interface to the CAN bus are not affected by soft
reset. The following registers are unaffected:
• CANx_CR
• CANx_RXGMASK
• CANx_RX14MASK
• CANx_RX15MASK
• all Message buffers
The SOFTRST bit can be asserted directly by the CPU when it writes to the CANx_MCR,
but it is also asserted when global soft reset is requested at MCU level. Because soft reset
is synchronous and has to follow a request/acknowledge procedure across clock domains,
it may take some time to fully propagate its effect. The SOFTRST bit remains asserted
while reset is pending, and is automatically negated when reset completes. Therefore,
software can poll this bit to know when the soft reset has completed.
0 No reset request
1 Resets values in registers indicated above.
7
FRZACK
Freeze mode acknowledge. Indicates that FlexCAN2 is in freeze mode and its prescaler is
stopped. The freeze mode request cannot be granted until current transmission and
reception processes have finished. Therefore the software can poll the FRZACK bit to
know when FlexCAN2 has actually entered freeze mode. If freeze mode request is
negated, then this bit is negated after the FlexCAN2 prescaler is running again. If freeze
mode is requested while FlexCAN2 is disabled, then the FRZACK bit will only be set when
the low power mode is exited. See
Section 22.4.6.1, “Freeze Mode
,” for more information.
0 FlexCAN2 not in freeze mode, prescaler running
1 FlexCAN2 in freeze mode, prescaler stopped
8–10
—
Reserved.
11
MDISACK
Low power mode acknowledge. Indicates whether FlexCAN2 is disabled. This cannot be
performed until all current transmission and reception processes have finished, so the CPU
can poll the MDISACK bit to know when FlexCAN2 has actually been disabled. See
Section 22.4.6.2, “Module Disabled Mode
,” for more information.
0 FlexCAN2 not disabled
1 FlexCAN2 is disabled
12–25
—
Reserved.
26–31
MAXMB
[0:5]
Maximum number of message buffers. This 6-bit field defines the maximum number of
message buffers of the FlexCAN2 module. The reset value (0x0F) is equivalent to 16 MB
configuration. This field should be changed only while the module is in freeze mode.
Note: MAXMB has to be programmed with a value smaller or equal to the number of
available message buffers, otherwise FlexCAN2 will not transmit or receive frames.
Table 22-7. CANx_MCR Field Descriptions (Continued)
Bits
Name
Description
Maximum MBs in use
MAXMB
1
+
=
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